In recent years, submerged and shroud nozzles have been widely used in the field of continuous casting of molten metals, in which an inert gas is blown into a molten metal, for the purpose of improving the quality of the cast products such as steel or of preventing the nozzles from being clogged up with materials adhered thereto.
An example of a submerged nozzle is described in the specification of Japanese Patent Application Laid-open No. 56-102357, which has a gas-blowing hollow chamber with an annular section in the axial direction of the nozzle body. A gas is blown from the hollow chamber into the molten metal flowing in the pouring hole of the submerged nozzle.
The gas-blowing hollow chamber is provided with bridges of a small diameter in the inner part thereof, whereby the breakdown of the hollow chamber due to the pressure of the molten metal can be prevented.
This hollow chamber is empty and therefore has the function of a heat-insulator between the axial part and the peripheral wall part, and causes remarkable temperature difference between the inner refractory part and the outer refractory part of the hollow chamber by its insulating effect, which results in yielding a thermal stress therebetween. Consequently, the refractory part in the outer wall of the hollow chamber is in danger of breakdown in spite of the provision of the reinforcing bridges therein.